WAVES, SOUND, AND LIGHT

S8P4. Students will explore the wave nature of sound and electromagnetic radiation.

a. Identify the characteristics of electromagnetic and mechanical waves.

b. Describe how the behavior of light waves is manipulated causing reflection, refraction, diffraction, and absorption. c. Explain how the human eye sees objects and colors in terms of wavelengths. d. Describe how the behavior of waves is affected by a medium (such as air, water, solids). e. Relate the properties of sound to everyday experiences. f. Diagram the parts of the wave and explain how the parts are affected by changes in amplitude and pitch.

S8P4- Elements a-f

The Energy of WavesA wave is any disturbance that transmits energy through matter or empty space. Waves transfer energy, have certain properties, and interact in predictable ways.

Energy Transfer Through a MediumMechanical waves transfer energy by the vibration of particles in a medium. A medium is a substance through which a wave can travel. A medium can be a solid, a liquid, or a gas.

Waves Can Transfer Energy Without a Medium

Some waves can transfer energy without going through a medium. Visible light is one example. Other examples include microwaves made by microwave ovens, TV and radio signals, and X rays used by dentists and doctors. These waves are electromagnetic waves.

Parts of a Wave

Types of Waves

• Waves in which the particles vibrate in an up-and-down motion are called transverse. .waves.

• In a longitudinal wave, the particles of the medium vibrate back and forth along the path that the wave moves.

All waves transfer energy by repeated vibrations. However, waves can differ in many ways. Waves can be classified based on the direction in which the particles of the medium vibrate compared with the direction in which the waves move. The two main types of waves are transverse waves and longitudinal waves.

Waves and SoundA sound wave is an example of a longitudinal wave. Sound waves travel by compressions and rarefactions of air particles. The photo shows how a vibrating drum forms compressions and rarefactions in the air around it.

Sound WavesA sound wave is a longitudinal wave caused by vibrations and carried through a substance. The particles of the substance, such as air particles, vibrate back and forth along the path that the sound wave travels. Sound is transmitted through the vibrations and collisions of the particles.

Sound and MediaAnother characteristic of sound is that all sound waves require a medium (plural, media). A medium is a substance through which a wave can travel. Most of the sounds that you hear travel through air at least part of the time. But sound waves can also travel through other materials, such as water, glass, and metal.

Reflection and Echo Reflection is the bouncing back of a wave after it strikes a barrier. A reflected sound wave is called an echo.

Frequency and PitchHow low or high a sound seems to be is the pitch of that sound. The frequency of a wave is the number of crests or troughs that are made in a given time.

The Doppler EffectFor sound waves, the Doppler effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound.

Amplitude and Loudness

Loudness is a measure of how well a sound can be heard. The amplitude of a wave is the largest distance the particles in a wave vibrate from their rest positions. The larger the amplitude, the louder the sound. And the smaller the amplitude, the softer the sound.

ResonanceResonance happens when a vibrating object causes a second object to vibrate also. When the strings vibrate, sound waves enter the body of the guitar. Standing waves form inside the body of the guitar, and the sound is amplified.

Waves and LightLight is an electromagnetic wave. Electromagnetic waves interact in predictable ways.

Electromagnetic WavesAn electromagnetic wave is a wave that can travel through empty space or matter and consists of changing electric and magnetic fields.

The Electromagnetic Spectrum

Visible Light From the Sun

Some of the energy that reaches Earth from the sun is visible light. The visible light from the sun is white light. White light is visible light of all wavelengths combined.

Colors of LightHumans see the different wavelengths of visible light as different colors. The longest wavelengths are seen as red light. The shortest wavelengths are seen as violet light.

Materials Matter

Reflection Reflection happens when light waves bounce off an object. Light reflects off objects all around you. When you look in a mirror, you are seeing light that has been reflected twice—first from you and then from the mirror.

RefractionRefraction is the bending of a wave as it passes at an angle from one substance, or material, to another. Refraction of light waves occurs because the speed of light varies depending on the material through which the waves are traveling.

Refraction and Optical illusionsUsually, when you look at an object, the light reflecting off the object travels in a straight line from the object to your eye. But when you look at an object that is underwater, the light reflecting off the object does not travel in a straight line. Instead, it refracts.

Prisms and RainbowsRefraction and Color SeparationWhite light is composed of all the wavelengths of visible light. The different wavelengths of visible light are seen by humans as different colors. When white light is refracted, the amount that the light bends depends on its wavelength. Color separation by refraction is responsible for the formation of rainbows. Rainbows are created when sunlight is refracted by water droplets.

DiffractionDiffraction is the bending of waves around barriers or through openings. The amount a wave diffracts depends on its wavelength and the size of the barrier or the opening.

Lenses